In general, medium access and/or scheduling is of outmost importance for the operation and performance of communication networks.
A contention-based protocol is a communications protocol for medium access and for operating wireless telecommunication equipment that allows many users to use the same radio-based medium with little or no pre-coordination.
Listen Before Talk, LBT, or sometimes called Listen Before Transmit is an example of a contention-based procedure for medium access used in radio communications whereby a radio transmitter first senses its radio environment, i.e. a radio based medium or channel, before it starts a transmission. Sometimes Listen Before Talk is referred to as Sense Before Transmit. The LBT operating procedure in IEEE 802.11 is one of the most well-known contention-based protocols.
For example, Carrier Sensing Multiple Access, CSMA, is a Medium Access Control, MAC, protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum.
Carrier Sensing means that a transmitter uses feedback from a receiver to determine whether another transmission is in progress before initiating a transmission. That is, it tries to detect the presence of a transmission or carrier wave from another station before attempting to transmit. If a transmission/carrier is sensed, the station waits for the transmission in progress to finish before initiating its own transmission. In other words, CSMA is also based on LBT. Multiple access means that multiple stations send and/or receive on the medium.
LBT is also proposed for use in cellular communication systems, such as LTE operating in unlicensed spectrum.
Reference [1] relates to a method and system for scheduling multiple concurrent transmissions during a contention access period in a wireless communications network. Communicating devices within a piconet are operable to derive a neighborhood map of the piconet. The neighborhood map information may enable a plurality of devices to concurrently transmit signals during a given channel time allocation time slot. The neighborhood map information may enable individual devices to set clear channel assessment thresholds. Individual devices may utilize threshold information to determine when to transmit signals to one or more destination devices and/or at what rate to transmit data via the signals.
Reference [2] relates to techniques to adaptively adjust a clear channel assessment threshold for use when a wireless device is to transmit in a wireless network that operates on a channel in a radio frequency band. A first wireless device, configured to wirelessly communicate with one or more second wireless device in the wireless network, receives energy on the channel in the frequency band, analyzes the received energy to detect interference on the channel and determines a type of interference detected in the received energy. The clear channel assessment threshold is adjusted by an amount depending on the type of interference detected.
Reference [3] relates to methods and corresponding systems for adapting a clear channel assessment threshold in a node in a wireless network by determining a first successful transmission rate of the node and neighboring nodes in the wireless network when the node is set to use a first threshold. Next, a second successful transmission rate of the node and the neighboring nodes is determined when the node is set to use a second threshold. Thereafter, one of the first and the second Clear Channel Assessment Thresholds, CCATs, is selected based upon the first and second successful transmission rates.
However, there is a general need to improve conventional medium access procedures such as LBT-based medium access, to provide higher system efficiency and/or better user quality.